1. Field of the Invention
The present invention relates to a radiation machine which acquires a radiograph from radiation transmitted through a subject, and more particularly to a technique of protecting an electronic component from exposure to radiation.
2. Description of the Related Art
In recent years, a digital X-ray imaging apparatus using, for example, a digital radiography (DR) system in which a captured image is instantly displayed on a monitor, is widely used. For still-image capturing, the digital X-ray imaging apparatus is portable. For movie capturing, a DR system supported by a stand is developed.
When a radiation detector is used to detect radiation, an integrated circuit (IC) is necessary to process a detected signal. When an IC chip, in which an integrated circuit is formed as a chip, is exposed to radiation during driving, degradation of a transistor in the IC may be progressed, resulting in a shorter life of the IC chip as compared with a case without radiation.
Japanese Patent Laid-Open Nos. 9-288184 and 2006-202791 disclose a configuration in which a protective member for absorbing and blocking radiation is arranged for every IC to prevent the IC from being degraded.
The protective member for the IC from exposure to radiation typically uses heavy metal, such as lead, molybdenum, or wolfram. To further efficiently protect the IC from exposure to radiation, the thickness of the heavy metal in a radiation direction is increased, to decrease transmittance of radiation. The degradation of the IC is proportional to a total exposure amount of radiation. Hence, as a frame rate during movie capturing is increased, the total exposure amount of radiation is increased. As a result, a member with increased thickness and weight is necessary for protecting the IC from exposure to radiation.
However, in radiographic imaging apparatuses disclosed in Japanese Patent Laid-Open Nos. 9-288184 and 2006-202791, when a detector for both still image and movie is used, the amount of a protective member in a casing is determined regarding movie capturing with a large amount of exposure to radiation. Owing to this, the casing including the protective member which expects movie capturing has to be carried even for still-image capturing, resulting in the weight being increased, and operation performance being decreased. In addition, the life of the IC may be restricted as long as the protective member should have a portable weight. The life of a product is not sufficient. It is noted that typical movie capturing requires a protective member by an amount five times that for still-image capturing. The increased weight may be a factor of decreasing the operation performance of image capturing while being carried.